System and method for labeling maps

ABSTRACT

A system and method for label placement is disclosed that achieves the twin goals of practical efficiency and high labeling quality by employing cartographic heuristics. A caller defines map and label properties. Then labels are pulled within a map boundary. Labels are next ordered by priority in descending importance. The order of testing labels is determined. Attempts are made to move overlapping labels. This is an iterative process; therefore there must be criteria that halt the procedure. Upon reaching an acceptable solution, the label properties are adjusted to reflect the new label placements.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/891,606, filed Aug. 13, 2007, which in turn is a continuation of U.S.patent application Ser. No. 10/462,044, filed Jun. 16, 2003, now U.S.Pat. No. 7,425,968, the entire file wrapper contents of which are herebyincorporated by reference as though fully set out at length.

COPYRIGHT NOTICE AND PERMISSION

This document contains some material which is subject to copyrightprotection. The copyright owner has no objection to the reproductionwith proper attribution of authorship and ownership and withoutalteration by anyone of this material as it appears in the files orrecords of the United States Patent and Trademark Office, but otherwisereserves all rights whatsoever.

FIELD OF THE INVENTION

The present invention relates to a computer-implemented method andapparatus for automatically labeling maps or graph layouts in accordancewith predefined label criteria.

BACKGROUND OF THE INVENTION

Maps include geographic drawings showing countries, cities, rivers,bodies of water, mountains, and other features of interest. Labelingcartographic features is a fundamental part of map-making. Placing eachlabel optimally with respect to its corresponding feature invariablyproduces labels overlapping each other or too close to each other. Asthis results in confusion and unacceptable maps, methods to repositionlabels or not draw them at all must be used to create a map that conveysas much information as possible.

Tagging graphical objects with text labels is a fundamental task in thedesign of many types of informational graphics. This problem is seen inits most essential form in cartography, but it also arises frequently inthe production of other informational graphics such as scatter plots.The quality of a labeling is determined essentially by the degree towhich labels obscure other labels or features of the underlying graphic.The goal is to choose positions for the labels that do not give rise tolabel overlaps and that minimize obscuration of features. Constructionof a good labeling is thus a combinatorial optimization problem, whichhas been shown to be NP-hard (Marks and Shieber, 1991).

As a hypothetical baseline algorithm, randomly choosing positions foreach label generates a poor labeling, both aesthetically, and asquantified using a metric that counts the number of conflicted labels,i.e., those that obscure point features or other labels.

In addition to geographical and technical maps, there are many labelingapplications relating to graph layouts and drawings. These applicationsinclude, but are not limited to, areas such as database design (e.g.entity relationship diagrams), software engineering including CASE,software debugging, complex web pages, CAD drafting, complex electricaldiagrams, and telecommunications and communications networking. In fact,the labeling of the graphical features of any drawing is generallynecessary because it conveys information essential to understanding thedrawing. For complex and information rich drawings, computer aidedlabeling is increasingly employed.

As used in the present specification, the term “map” is used to includeboth geographical and technical maps as well as graph layouts anddrawings. The term “label” is used to refer to text or other indicia tobe placed on a map.

A system and method for labeling objects on maps while avoidingcollisions with other labels has been sought after. Some apparentlypowerful algorithms for automatic label placement on maps use heuristicsthat capture considerable cartographic expertise but are hampered byprovably inefficient methods of search and optimization.

This patent discloses a system and method for label placement thatachieves the twin goals of practical efficiency and high labelingquality by employing cartographic heuristics.

SUMMARY OF THE INVENTION

The present invention provides a computer-implemented system and methodof automatically labeling a map in accordance with predefined labellocation, placement, and priority criteria.

Here, each label is represented as a convex polygon with any orientationon the map. Labels have various parameters associated with them such aslocation, size, shape, number and location of vertices, target feature,priority, movement constraints, and clearance. After finding the bestposition of a label for every feature without regard to other labels orfeatures, higher priority label positions are compared to lower prioritylabel positions two at a time. If the labels interfere, the lowerpriority label is moved within its movement constraint. Severalcandidate locations for the lower priority label position are found bymoving it the shortest distance to avoid the higher priority labelposition. A new location is acceptable if the location does not collidewith a label of higher priority. It can collide with a label of lowerpriority. If no candidate positions are acceptable, the label is notmoved. This process continues until all labels are inspected, afterwhich a deviation from the desired result function is calculated. Thisfunction is zero if the label interference for all labels is zero andgreater than zero otherwise. The whole process is repeated until theevaluation function equals zero or the change in the evaluation functionis less than a given percent (e.g., two percent) for a small number(e.g., four) of iterations or if it oscillates for a number (e.g., six)of iterations or if the number of iterations is greater than a setnumber (e.g., twenty). If any interference remains, then interferinglabels with lower priorities are not drawn.

The details of the present invention, both as to its structure andoperation, can best be understood in reference to the accompanyingdrawings, in which like reference to the accompanying drawings, in whichlike reference numerals refer to like parts, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a computer hardware architecture compatible withthe present system and method.

FIG. 2 is a schematic diagram showing an exemplary computer programproduct.

FIG. 3 is a flow chart showing the overall logic of the present systemand method.

FIGS. 4a, 4b, and 4c is a flow chart showing the initialization of theanti-collision system and method.

FIG. 5 is a flow chart of the sorting labels by priority.

FIG. 6 is a flow chart showing the initialization of halting criteriavariables.

FIGS. 7a and 7b is a flow chart showing the test of whether each labelhas been tested.

FIG. 8 is a flow chart showing the overlap test.

FIGS. 9a, 9b, and 9c is a flow chart showing the movement procedure.

FIG. 10 is a flow chart showing the initiation of collision scores andpriority ranges.

FIG. 11 is a flow chart showing the calculation of the evaluationfunction.

FIG. 12 is a flow chart showing the halt routine.

FIG. 13 is a flow chart showing the routine to adjust label properties.

FIG. 14 is a flow chart showing the return to caller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, a system is shown which includes adigital processing apparatus. This system is a general-purpose computer1000. The computer may include a graphics display, print hardware, andprint software, or may be as simple as a generic personal computer. Theexample computer in FIG. 1 includes central processor 1010, systemmemory 1015, disk storage 1020 (e.g., hard drive, floppy drive, CD-ROMdrive, and DVD drive), controller 1005, network adapter 1050, videoadapter 1030, and monitor 1055. Data input may be through one or more ofthe following agencies: keyboard 1035, pointing device 1040, diskstorage 1020, local area network 1060, point to point communications1065, and wide area network 1070 (e.g., internet).

One or more features of the computer as shown may be omitted while stillpermitting the practice of the invention. For example, printer 1045 isnot necessary for maps intended to be displayed only on monitor 1055.Likewise, network adapter 1050, local area network 1060, point to pointcommunications 1065, and wide area network 1070 are not necessary whenthe primary method of data input is via removable disk storage.

The flow charts herein illustrate the structure of the logic of thepresent invention as embodied in computer program software. Thoseskilled in the art will appreciate that the flow charts illustrate thestructures of logic elements, such as computer program code elements orelectronic logic circuits, that function according to this invention.

Manifestly, the invention is practiced in its essential embodiment by amachine component that renders the logic elements in a form thatinstructs a digital processing apparatus (that is, a computer) toperform a sequence of function steps corresponding to those shown.

FIG. 2 shows a computer program product which includes a disk 1080having a computer usable medium 1085 thereon for storing program modulesa, b, c, and d. While 4 modules are shown in FIG. 2, it is to beunderstood that the number of modules into which the program is dividedis arbitrary and may be in any particular embodiment a different number.

Modules a, b, c, d may be a computer program that is executed byprocessor 1010 within the computer 1000 as a series ofcomputer-executable instructions. In addition to the above-mentioneddisk storage 1020, these instructions may reside, for example in RAM orROM of the computer 1000 or the instructions may be stored on a DASDarray, magnetic tape, electronic read-only memory, or other appropriatedata storage device. In an illustrative embodiment of the invention, thecomputer-executable instructions may be lines of compiled C++ code.

FIG. 3 is an overview and summary of the label anti-collision procedurefor maps. The caller of the procedure performs the first stage, routine5, and the second stage, routine 8. Routine 5 involves locating eachlabel on a map in the optimal position with respect to its targetfeature without regard to other labels or features. Routine 8 assignsproperties to the map and the labels.

To begin, the user must specify how to initially place labels on a map.That is, commencing at routine 5, it is assumed that the user willassign positions that give the best label location with respect to itsassociated feature. For this procedure to work, the user places thelabels in the best spots according to their criteria regardless of otherlabels and map features. For example, in the initial positions, labelsmay overlap each other and/or extend over the map boundary. Labels areassumed to be convex polygons while the map boundary is assumed to be arectangle.

Next, at routine 8, the user must assign properties to the map and thelabels. Map properties include its height and width. A label'sproperties include the associated map feature(s), initial location,size, shape, angular orientation, priority, movement constraints, andclearance. In addition, each label has an associated property thatindicates the fraction of the label area that can extend outside the mapboundary before it is not drawn. The procedure takes all of theseproperties into account to move labels to acceptable positions or to notdraw the label.

The following discussion concerns only those geometric objects in theplane of the map, of which the labels are a part. All labels arerestricted to convex planar polygons in this plane. A planar polygon isconvex if it contains all the line segments connecting any pair of itspoints. If two convex planar polygons overlap, this means that:

-   -   1) at least one vertex of one polygon is inside the other        polygon, or    -   2) at least one edge of one polygon crosses or touches (i.e.,        intersects) an edge of the other polygon.

To begin the anti-collision procedure, three initialization steps occur.First, labels lying partially inside the map boundary must either bemoved completely inside the portrait or be excluded from being comparedto other labels and excluded from being drawn. Each label has movementtypes and constraints that determine whether or not the label qualifiesfor movement completely onto the map. These movement types andconstraints are explained below. Labels qualifying for movement to theinside of the map are moved regardless of the collision status with anyother label.

Second, the labels must be ordered in a list with respect to priorityfrom highest priority to lowest priority. In general, many labels willhave the same priority. Within any group of labels with the samepriority, any particular label is randomly placed within that block.

Third and last, variables that monitor the state of the procedure mustbe initialized.

The purpose of routine 10 is to move labels within the map boundary. Iftoo much of a label is outside the boundary, it will not be included inthe map. Each label is tested to determine what fraction of its area iswithin the map boundary.

At routine 20, labels are sorted in order of descending priority.Halting criteria parameters are initialized at routine 30.

Every combination of two labels is tested for overlap in routine 40.When comparing labels to determine if they overlap, it is important tochoose the order of comparison properly to avoid excessive calculationand moving labels more times than necessary. The highest priority labelsshould be tested for overlap before labels of lower priority.

The overlap test at routine 45 has three parts. First, it must bedetermined if any vertex of a first label is inside the second label.Second, it must be determined if any vertex of a second label is insidethe first label. Third, it must determine if any edge of the first labelintersects any edge of the second label. If at any point either label isdetermined to overlap the other label, then any remaining parts arebypassed.

Labels are moved about the map at routine 50 to clear existing labelcollisions. After it is determined that two labels overlap, the routinefinds several new locations for the lower priority of the two labelsthat eradicate the existing overlap. These locations are ranked by howfar the label must be moved, shortest to longest. Then if appropriate,the lower priority is moved to a new location, and its locationparameters are adjusted.

The evaluation function, routine 60, quantifies the extent of labelcollisions. Routines 40, 45, 50, and 60 iterate until halt routinecriteria 70 are satisfied. Labels may move several times before theiterations stop.

After the iterations stop, all labels are examined for any overlap andlabel properties are adjusted at routine 80. Finally, control isreturned at routine 90 to the user to draw or view the map.

FIGS. 4a, 4b, and 4c display the logic of routine 10 in detail. Thepurpose of routine 10 is to make sure all of a label is within the mapboundary. If too much of a label is outside the boundary, it will not beincluded in the map. Each label is tested to determine what fraction ofits area is within the map boundary. A particular label is divided intoa grid; 32 by 32 cells is a typical division that works well inpractice. If the centroid of a cell is within the map boundary, theentire cell contributes to the fraction of the label within theboundary. The areas of each cell within the map are added to together.If this sum of cell areas, divided by the total label area, is greaterthan a predetermined value, then the label is moved entirely onto themap according to the movement procedure and the movement constraintsdescribed below. The only change to the procedure is that there is notest for overlap with other labels. The qualifying labels are moved ontothe map at this time and tested later.

Step 100 obtains a list of labels from data storage. Each label istested for whether the entire label is inside the map boundary. First,step 108 initializes flags that will be used in routine 10. Step 112tests whether vertices of each label are outside the map boundary. Ifthe vertices of a label are all inside the map boundary, then the nextlabel is tested. If any vertices of a label are outside the mapboundary, then, at step 116, a circumscribing rectangle is placed aroundthe label. Then the circumscribing rectangle is divided into a pluralityof cells at step 120. For example, the rectangle may be divided into 64cells by 64 cells forming a total of 4096 cells.

Each cell is tested, step 124. The test includes finding the centerpoint of each cell to find the number of cells inside the label, step128. Then, at step 132, the center point of each cell used to find thenumber of cells both inside the label and inside the map.

The fraction of the label inside the map boundary is determined at step136. The high and the low values of the x and y coordinates for thevertices of the label are found in step 140. Then the label is tested,step 144, to determine if the fraction of the label inside the mapboundary is high enough to qualify for attempted movement inside themap. There is one of two possible ways the label might move depending onits movement constraints, which is determined in step 148. One movement,in both the x-axis and y-axis direction, is performed in steps 152, 156,160, 164, and 168. In step 152, the x-axis and y-axis movement of thelabel in the plane of the map (2D type movement) is initialized to(0,0). In step 156, the minimum 2D type movement to move the entirelabel within the map is determined (see the following pseudo-code forRoutine 10 which shows how to determine the minimum 2D type movement).

In step 160, the maximum allowed 2D movement parameter for the labelfrom its original position is compared to the minimum 2D type movement.In step 164, it is determined if the label fits within the map boundaryafter the label has been moved by the minimum 2D movement. This isreally a test to see if the label is too big to fit in the map. In step168, if the label can fit in the map, a label flag and a label parameterare set.

The other movement, restricted to a vector, is performed in steps 172,176, 180, 184, and 188. In step 172, the vector type label movementcandidates(s) to move the label within the map is determined (see thefollowing pseudo-code for Routine 10 which shows how to determine theminimum vector movement). In step 176, a loop cycles throughcandidate(s) for the label which are determined in step 172. In step180, if the maximum allowed vector movement parameter for the label fromits original position is less than the magnitude of the currentcandidate for the label, go to step 176. Otherwise, go to step 184. Instep 184, if the label does not fit within the map boundary after thelabel has been moved by the current candidate, go to step 176. This isreally a test to see if the label is too big to fit in the map.Otherwise, go to step 188. In step 188, if the label can fit in the map,a label flag and a label parameter are set. If the label is partially ortotally outside the map, and cannot be properly moved within the map,which is checked in step 192, then a parameter for that label is set instep 196.

Once all labels have been tested, step 104 exits routine 10 and proceedsto routine 20.

Referring to FIG. 5, labels are sorted by priority at step 200 from thehighest priority label to the lowest priority label and placed into adata structure map. Step 210 exits routine 20 and proceeds to routine30, an initialization of halting criteria variables.

In FIG. 6, step 300 initializes halting criteria variables. Step 310exits routine 30 and proceeds to routine 40, a test of every combinationof two labels for overlap.

The above-described logic is further shown in the following pseudo-codewith comments:

Referring to FIGS. 7a and 7b , labels are compared to determine if theyoverlap (routine 40). The number of labels and the maximum numericaldifference between the highest and lowest priority labels is determinedin step 400. All labels are grouped according to priority.

In step 403, a loop cycles through all the priorities from the highestpriority (i.e. priority 0) to the lowest priority of the labels (i.e.priority last_Pri), for every integer from 0 to last_Pri. In step 406,it is determined if there are any labels corresponding to the currentpriority in the loop. If there are no labels with the current priorityof the loop, then in step 409, set the value of arrayfirst_label[current priority of loop] to −1 and set the value of thearray last label [current priority of loop] to −1. If there are labelswith the current priority of the loop, then in step 412, set the valueof array first_label [current priority of loop] to the index of the mostimportant label with priority p and set the value of the arraylast_label [current priority of loop] to the index of the leastimportant label with priority p.

It is important to choose the order of comparison properly to avoidexcessive calculation and moving labels more times than necessary. Steps415, 421, 424, 427, 430, 436, and 442 perform cycling through labelpairs. This part compares two labels using loops. In step 415, the loopfor the first label starts at priority 0 and goes to priority last_Pri.In step 421, if the value of the variable:

first_label [current priority of first loop] is equal to −1, then goback to the beginning of loop for the first label. Otherwise, go to step424.

In step 424, the loop for the second label starts at the currentpriority of the first loop and goes to priority ‘last_Pri.’ In step 427,if the value of the variable:

-   -   first_label [current priority of second loop]        is equal to −1, then go back to the beginning of loop for the        second label. Otherwise, go to step 430.

In step 430, a third loop starts at the index in the list of labels ofthe first label with a priority equal to the current priority of thefirst loop and goes to the index in the list of labels of the last labelwith a priority equal to the current priority of the first loop. In step433, if the label with the current index in the list of labels from theloop in step 430 is completely outside of the map or too much of thelabel is outside of the map, then go back to step 430. Otherwise, go tostep 436.

In step 436, a fourth loop starts at the index in the list of labels ofthe first label with a priority equal to the current priority of thesecond loop and goes to the index in the list of labels of the lastlabel with a priority equal to the current priority of the second loop.When step 436 has finished examining the relevant labels, then step 436returns to step 430. As discussed above, when step 430 has finishedexamining the relevant labels, then step 430 returns to step 424. Ifstep 426 has not finished examining the relevant labels, then proceed tostep 439. In step 439, if the label with the current index in the listof labels from the loop in step 436 is completely outside of the map ortoo much of the label is outside of the map, then go back to step 436.Otherwise, go to step 442. In step 442, if the current label index ofthe loop in step 430 is less than or equal to the current label index ofthe loop in step 436, then go to step 436. Otherwise, go to step 445.

Step 445, which corresponds to routine 45, tests for overlap between themembers of the pair. Step 448, which corresponds to routine 50, performsthe movement procedure on one of the labels if they overlap. Step 418exits routine 40 and proceeds to routine 60, an evaluation functionprocedure.

The above-described logic is further shown in the following pseudo-codewith comments:

Order of Comparison for the Label Overlap Test Routine // The n labelshave already been sorted in priority order, // from the most important,label 0, consecutively, // to the least important, label (n - 1).LABEL_TOO_MUCH_OUTSIDE_PORTRAIT - indicates if the procedure hasdetermined that the label has much area outside the map boundary or cannot be properly moved to a new position completely inside the mapboundary. This is a flag of every label set by the procedure.LABEL_OUTSIDE_PORTRAIT - Not used. This is a flag of every label set bythe procedure. LABEL_MOVED_INTO_PORTRAIT - indicates if the procedurehas moved a label that was originally partially outside the map boundaryto a new position completely inside the map boundary. This is a flag ofevery label set by the procedure. last_Label_Index = number_of_labels -1; // zero based // Zero based. // The highest priority is zero and thelowest priority is a number greater than zero. // Note that there may bepriorities which have no labels. Last_Pri = lowest priority - highestpriority; // which equal the lowest priority // Below, if there are nolabels with priority p, // first_Pri[p] = −1 and last_Pri[p] = −1 //first_label[p] = first label index with priority p // last_label[p] =last label index with priority p for p = 0 to last_Pri; // highestpriority to lowest priority  if labels with priority p exist  first_label[p] = most important label with priority p;   last_label[p]= least important label with priority p;  Else   first label[p] = −1;  last_label[p] = −1; next p; for i_pri = 0 to last_Pri; // highestpriority to lowest priority  if first_label[i_pri] = −1, continue tonext i_pri;  for j_pri = i_pri to last_Pri; // highest priority tolowest priority   if first_label[j_pri] = −1, continue to next j_pri;  for i_idx = first_label[i_pri] to last_label[i_pri];   if i_idx flagLABEL_TOO_MUCH_OUTSIDE_PORTRAIT = TRUE      OR LABEL_OUTSIDE_PORTRAIT =TRUE, continue to    next i_idx for j_idx = first_label[j_pri] tolast_label[j_pri];     // Do not compare a label to itself or     //compare labels which have been previously compared,     // for thisparticular iteration of the entire algorithm.     if i_idx <= j_idx,continue to next j_idx;     if j_idx flagLABEL_TOO_MUCH_OUTSIDE_PORTRAIT =      TRUE OR LABEL_OUTSIDE_PORTRAIT =TRUE, continue      to next j_idx if label i_idx overlaps label j_idx,     then perform the label movement procedure on label j_idx;    nextj_idx;   next i_idx;  next j_pri; next i_pri;

All labels are restricted to convex planar polygons in the plane of themap. A planar polygon is convex if it contains all the line segmentsconnecting any pair of its points. If two convex planar polygonsoverlap, this means that:

1) at least one vertex of one polygon is inside the other polygon, or

2) at least one edge of one polygon intersects an edge of the otherpolygon.

Routine 45, shown in FIG. 8, is a label overlap test procedure. Theoverlap test has three parts. First, it determines if any vertex of thefirst polygon is inside the second polygon, step 462. Second, itdetermines if any vertex of the second polygon is inside the firstpolygon, step 466. Third, it determines if any edge of the first polygonintersects any edge of the second polygon, step 470. Once any vertex isfound to be inside the other polygon, there is no need to test remainingvertices and edges. Once any edge is found to intersect any edge of theother polygon, there is no need to test remaining edges and vertices.

Prior to the overlap test, routine 45 begins by receiving two labelsfrom caller in step 450. In step 454, the maximum and minimum x and yvalues for each label are determined. These x and y values formcircumscribing rectangles, whose edges are parallel to the map's x axisand y axis, for each label. In step 458, the circumscribing rectanglesfor each label are compared. If these circumscribing rectangles do notoverlap, then routine 45 returns “no overlap” to the caller in step 478.

FIG. 8 shows the test for whether a vertex of a polygon is insideanother polygon. The method is shown in “Determining if a Point Lies onthe Interior of a Polygon,” Paul Bourke (available on the world wideweb). Consider the standard right-handed two-dimensional Cartesiancoordinate system with the positive y direction up and the positive xdirection to the right. A first polygon's edges are chosen such that theperimeter is traversed in the counterclockwise (CCW) direction (theperimeter may be traversed in a clockwise direction so long as it isdone consistently). At step 462, if any vertex of a second polygon is tothe left of all edges of the first polygon, then that vertex is insidethe first polygon. Likewise, at step 466, if any vertex of the firstpolygon is to the left of all edges of the second polygon then thatvertex is inside the second polygon. If any vertex of a polygon isinside another polygon, then the polygons overlap. This is the test fora point being inside a convex planar polygon.

Lines containing the edges that make up a polygon may be written,(y−Y1)(X2−X1)−(x−X1)(Y2−Y1)=0where(x,y) is any point on the line, and(X1,Y1) and (X2,Y2) are the endpoints of an edge of the polygon undertest. Points lying on the polygon edges satisfy the line equations,while points not on the polygon edges do not satisfy those equations. If(x, y) is any point in the plane, the equation for a line containing anedge is:(y−Y1)(X2−X1)−(x−X1)(Y2−Y1)=Kwhere K is a real number constant.

Then, for all points to the left of any edge, K>0, and for all points tothe right of any edge, K<0. Note that point 2 in the above equation isat the head of the vector representing the edge and point 1 is at thetail of the vector representing edge. This is true because, for alledges pointing to the right, (X2−X1)>0. For any point above the linecontaining the edge, (x_above, y_above), there exists a point, (x,y), onthe line, such that:x_above=x and y_above>yTherefore:(y−Y1)(X2−X1)−(x−X1)(Y2−Y1)=(y−Y1)(X2−X1)−(x−X1)(Y2−Y1)(y_above−Y1)(X2−X1)−(x−X1)(Y2−Y1)>(y−Y1)(X2−X1)−(x−X1)(Y2−Y1)(y_above−Y1)(X2−X1)−(x_above−X1)(Y2−Y1)>(y−Y1)(X2−X1)−(x−X1)(Y2−Y1)

A point that is above a line pointing to the right is a point that liesto the left of the line. Similar arguments show that any point on theleft of lines pointing up, pointing down, or pointing left yields apositive value with substituted into the line equation.

Step 470 tests whether the edges of one polygon intersect anotherpolygon. Consider the equations of the lines that contain the edges ofthe first polygon and the equations of the lines that contain the edgesof the second polygon. Determine the intersection point for everytwo-line combination, where one line is a line that contains an edge ofthe first polygon and the other line is a line that contains an edge ofthe second polygon. If the intersection point lies on or between theendpoints of the polygon edges, then the edge of one polygon intersectsthe edge of the other polygon and the polygons overlap. In cases wherethe lines are parallel, and not coincident, no intersection point existsfor that pair of lines. If the lines are coincident, then the edges mayor may not touch, but if the edges touch then the polygons overlap.

If the three above overlap tests, at step 462, step 466, step 470, findan overlap between the two labels, then routine 45 returns “labelsoverlap” to the caller in step 482, step 486, and step 490,respectively. If after performing the three tests, there is no overlapbetween the two labels, then routine 45 returns “no overlap” to thecaller in step 474.

The above-described logic is further shown in the following pseudo-codewith comments:

Pseudo-code for the Overlap Test of Convex Planar Polygons List ofpseudo-code variables (x_2_i, y_2_1) - vertex i of polygon 2 (X1_j,Y1_j) - vertex 1 of edge j of polygon 1 (X2_j, Y2_j) - vertex 2 of edgej of polygon 1 (x_IP, y_IP) - intersection point of lines containingedges x_max_i - max x of edge i y_min_j - min y on edge j find max x,max y, min x, min y on polygon 1 - each will be on a Vertex find max x,max y, min x, min y on polygon 2 - each will be on a vertex // if anyexpression is true, the polygons do not overlap, so return False if (minx of polygon 1 >= max x of polygon 2) RETURN NO_OVERLAP if (min x ofpolygon 2 >= max x of polygon 1) RETURN NO_OVERLAP if (min y of polygon1 >= max y of polygon 2) RETURN NO_OVERLAP if (min y of polygon 2 >= maxy of polygon 1) RETURN NO_OVERLAP // if any vertex of polygon 2 isinside polygon 1, the result is greater than zero. // proceed aroundpolygon 1 in the CCW direction for each vertex of polygon 2 for i =first vertex of polygon 2 to last vertex of polygon 2  inside = TRUE for j = first edge of polygon 1 to last edge of polygon 1 in CCWDirection   if((y_2_i - Y1_j) (X2_j - X1_j) - (x_2_i - X1_j) (Y2_j -Y1_j) <= 0) inside = FALSE  next j  if (inside = TRUE), RETURN OVERLAPnext i Repeat the above, except test polygon 1 vertices with polygon 2edges Return OVERLAP if appropriate // perform the edge intersectiontest for i = first edge of polygon 1 to last edge of polygon 1  of thetwo endpoints of edge i, get x_max_i, y_max_i, x_min_i, y_min_i  for j =first edge of polygon 2 to last edge of polygon 2   of the two endpointsof edge j, get x_max_j, y_max_j, x_min_j, y_min_j   solve forintersection point, (x_IP, y_IP), of lines containing edge i and edge j  if intersection point exists    // An intersection at an endpoint isan overlap.    // These tests also take care vertical and horizontaledges.    if (x_IP <= x_max_i and x_IP >= x_min_i) and     (y_IP <=y_max_i and y_IP >= y_min_i) and     (x_IP <= x_max_j and x_IP >=x_min_j) and     (y_IP <= y_max_j and y_IP >= y_min_j), RETURN OVERLAP next j next i RETURN NO_OVERLAP

Labels must be moved about the map to clear existing label collisions.After it is determined that two labels overlap, routine 50 (FIGS. 9a,9b, and 9c ) finds several new locations for the lower priority of thetwo labels that eradicate the existing overlap. The higher prioritylabel is a first label while a lower priority label is a second label.These locations are ranked by how far the second label must be moved,shortest to longest. The actual location finally selected must meet thefollowing criteria:

-   -   1) the second label moves a shorter distance than other        qualifying locations;    -   2) the second label movement does not result in overlap with        another label (or labels) of equal or higher priority than the        first label;    -   3) the second label movement does not exceed the maximum        movement parameters    -   4) for that particular label; and    -   5) no part of the second label is moved outside the map        boundary.

If no candidate locations meet these criteria, the second label is notmoved. During the process of fixing existing collisions, othercollisions may be created. New collisions are only allowed if it reducescollisions among labels with priorities equal to or higher than thefirst label. As the procedure iterates, new collisions are handled likethe original collisions. The procedure will minimize collisions.

Each label may be moved in one of two ways. A caller selects the type ofmovement of a label to the exclusion of the other type of movement.First, a label may move in any direction on the map, up to a maximumdistance from the original location. This is referred to as 2D typemovement. Second, a label may move parallel to a vector up to a maximumdistance from the original location in the positive vector direction orthe negative vector direction. This is referred to as vector typemovement that may be used for linear features such as highways andrivers. Both the vector and the maximum distances are in the label'sparameter list. Labels on a map may consist of any mixture of 2Dmovement and vector movement types. However, higher priority labels mustbe examined before lower priority labels regardless of movement type.

Prior to the attempted label movement, routine 50 begins by receivingtwo labels from caller in step 500. Routine 50 cycles through the edgesof first label in step 503 and cycles through the vertices of secondlabel in step 509. A counter is set in step 506.

The first label's edges are traversed in a CCW direction. Rememberingthat these operations take place on a two dimensional map, step 512tests whether each vertex of the second label is left of a linecontaining an edge of the first label when the first label is traversedin a CCW direction. A vertex of the second label is said to be on alabel side of the line containing the edge of the first label if thevertex of the second label and area of the first label are on the sameside of the line containing the edge of the first label. Note that theselabels are restricted to convex polygons so all of one label will be onone side of the line containing the label's edge and no part of thelabel will be on the other side of the line. Likewise, a vertex of asecond convex polygon is said to be on a convex polygon side of a linecontaining an edge of a first convex polygon if the vertex of the secondconvex polygon and area of the first convex polygon are on the same sideof the line containing the edge of the first convex polygon. If step 515specifies a 2D type movement, then step 518 finds an intersection of twolines. A first line is the line that contains one edge of the firstlabel. A second line is perpendicular the first line and contains thevertex. If, instead, step 515 specifies a vector type movement, thenstep 521 finds an intersection of a line containing an edge and a lineparallel to the vector type movement also containing the vertex.

If in either the 2D type movement case or the vector type movement case,an intersection exists, step 524, and the vertex is on the label side asdefined above, step 527 calculates a first vector from the vertex to theintersection. If the first vector is too small, step 530, then theroutine 50 calculates, in steps 533, 536, and 539, a second vector withdesirable properties listed in steps 536 and 539. In the case that thefirst vector is too small, the first vector is replaced by the secondvector. Whichever vector remains, it is hereafter referred to as thevector.

Step 542 tests whether the vector is within movement bounds from theoriginal label location. If at step 545, it is within bounds, the vectoris placed on an end of a list of qualified vectors and a length of thevector is placed on an end of a length list. Once all vertices of thesecond label are tested, if there any qualified vectors (step 548),then, at step 551:

-   -   1) Find the maximum length in the length list and a        corresponding qualified vector from the vector list;    -   2) Insert the length and the qualified vector into a data        structure map that is sorted by distance; and    -   3) Empty the length list and vector list.

After all the edges of the first label are checked, at step 554 thesteps starting at step 512 are repeated using the edges of the secondlabel and the vertices of the first label. For any qualifying vectors, anegative of the vector is taken and that vector and its length areinserted into the data structure map.

Next, tests are performed to determine if proposed locations for thesecond label are acceptable. At step 560, starting with a shortestvector in the data structure map, the second label is moved in both adirection and a length of the shortest vector to obtain a new locationfor the second label. Then, at step 563, a test is performed todetermine if part of the new location for the second label is outsidethe map boundary. If, the new location for the second label places partof the second label outside the map boundary, repeat steps 557, 560, and563, using a next vector from the data structure map. Step 566 retrieveslabels with priorities greater than or equal to the first label. In step569, if any retrieved label is the first label or the second label, thenretrieve the next label in step 566. At step 572, the overlap test isperformed on the current candidate location for the second label againstlabels that fail tests at step 563 and step 569. If there is an overlap,steps 557 through 572 are repeated. Otherwise, the second label is movedto the candidate location in step 575. After a new location is found forthe second label among the proposed locations, or after all proposedlocations are determined to be unacceptable, then data structure map iscleared in step 578, and a next pair of labels is supplied in step 581.

The above-described logic is further shown in the following pseudo-codewith comments:

Movement Procedure of Convex Planar Polygons // List of pseudo-codevariables (x_2_j, y_2_j) - vertex j of polygon 2 (X1_i, Y1_i) - vertex 1of edge i of polygon 1 (X2_i, Y2_i) - vertex 2 of edge i of polygon 1(x_IP, y_IP) - intersection point of lines containing edge and vertex(X,Y) - vector from vertex to edge pseudo-code also has:  a list ofdistances  a list of vectors  a data structure map of distances andvectors sorted by distance, short to long // Polygon 1 is the moreimportant polygon and polygon 2 will move if possible // Here, thevertices in a polygon are on the left side of the edge // of the otherpolygon when traversing it in the CCW direction, // but the vertices arenot necessarily inside the other polygon. // That is why allpossibilities are caught in the algorithm below - // even where novertex from either polygon is inside the other. // Do not have to checkspecifically for the above case. // If a vertex of polygon 2 is on leftside a polygon 1 edge, the result is greater than zero. // proceedaround polygon 1 in the CCW direction for each vertex of polygon 2 //Note the the vertex in question does not have to be inside polygon 1 fori = first edge of polygon 1 to last edge of polygon 1 in CCW Direction count_of_possible_vertices = 0  for j = first vertex of polygon 2 tolast vertex of polygon 2   if((y_2_j - Y1_i) (X2_i - X1_i) - (x_2_j -X1_i) (Y2_i - Y1_i) > 0)    if (2D type movement for polygon 2)     // asolution will always exist for this case     solve for intersectionpoint, (x_IP, y_IP), of a line containing edge i     and a lineperpendicular to edge i containing (x_2_j, y_2_j)    if (vector typemovement for polygon 2)     // a solution might not exist for this case    solve for intersection point, (x_IP, y_IP), of a line containingedge i     and a line parallel to the vector type movement containing(x_2_j, y_2_j)    if ( solution exits for (x_IP, y_IP) )     // getvector from vertex to intersection point     (X,Y) = (x_IP - x_2_j,y_IP - y_2_j)     if ( (X,Y) length minute )      if ( 2D type movementfor polygon 2 )       find a point (X,Y) which meets the followingrequirements        on right side of edge i (CCW)        contained by aline perpendicular to edge i        contained by a line also containing(x_IP, y_IP)        a minute distance from (x_IP, y_IP)      else //vector type movement for polygon 2       find a point (X,Y) which meetsthe following requirements        on right side of edge i (CCW)       contained by a line parallel to the vector type movement       contained by a line also containing (x_IP, y_IP)        a minutedistance from (x_IP, y_IP)     // because polygon may move severaltimes, keep the original location of the label     if ( movement of(X,Y) leaves polygon with movement limit )      // Make vector just abit larger that the distance to the edge      // so when polygon 2 ismoved, it moves just outside the      polygon 1      length_of_XY =length of (X, Y) * (1.0 + 1.0e−09)      X = X * (1.0 + 10e−09)      Y =Y * (1.0 + 10e−09)      append length_of_XY to end of distance list     append (X,Y) to end of vector list      count_of_possible_vertices= count_of_possible_vertices + 1  next j  if(count_of_possible_vertices > 0)   find the maximum distance in thedistance list   get the corresponding vector to this distance from thevector list   insert the distance and the vector into the data structuremap sorted by distance,   from the shortest distance to the longestdistance   empty distance list and vector list next i Repeat the above,except use polygon 1 vertices and with polygon 2 Edges The vector forpossible movement, (X,Y), is reversed Insert the results into the samedistance/vector data structure map // the outer loop is just goingthought the sorted data structure map for i = first location candidateto last location candidate   get new location for polygon by addingvector (X,Y) to each vertex   if ( any part of label outside mapboundary ) next i   for j = first label to last label whose priority >=polygon 1    if ( polygon 1 is label j or polygon 2 is label j) next j   if ( polygon 2 in location candidate i overlaps label j ) next i   update polygon 2 location in its parameter list    break out of bothfor loops  next j next i clear the data structure map get the next pairof labels to be tested for overlap

The Evaluation Function, the Halting Criteria, and the Adjustment ofLabel Properties

The following pseudo-code contains a reminder to initialize collisionscores and priority ranges at the top of the procedure. This is shown inFIG. 10, assignment 590. It is probable that the process of labelmovement will iterate indefinitely, therefore halting criteria areneeded. An evaluation function provides input to a halting procedure tostop the process at an acceptable point. The calculation of theevaluation function is represented by routine 60 as shown in FIG. 11.All labels that overlap are known at this point. The procedure used toreduce label collisions is an iterative process. A collision score is avariable that measures the severity of collisions of labels in the map.It is initialized to zero in step 600. Step 605 performs cycling throughlabel pairs. In step 610, each label of the current pair of labels istested to see if it has too much of its area outside the map or if it iscompletely outside the map. This avoids unnecessary calculation forlabels that will not be used. The overlap test (routine 45) is performedin step 615. If no overlap occurs between the two labels being tested,then another unique pair of labels is fetched in step 605. If overlapoccurs, then the collision score is added to the previous collisionscore in step 620. The final value of the collision score is attainedafter all the unique label pairs have been tested. In thisanti-collision procedure for maps, the evaluation function at step 620is: Collision Score=

${{Collision}\mspace{14mu}{Score}}\; = {\sum\limits_{\overset{\_}{i}j}\left( {\left( {{label}\mspace{14mu} i\mspace{14mu}{adjusted}\mspace{14mu}{priority}} \right)^{2} + \left( {{label}\mspace{14mu} j\mspace{14mu}{adjusted}\mspace{14mu}{priority}} \right)^{2}} \right)}$where the score is the summation over every pair of overlapping labels.The result of this function is defined as zero if no collisions remainand greater than zero if any collisions remain. The function penalizesdisproportionately for collisions involving high priority labels. Forinstance, a collision involving a high priority label and a low prioritylabel gets a higher score (worse) than a collision involving two mediumpriority labels.

Routine 70 as shown in FIG. 12 evaluates halting criteria to determineif the labels are in optimal locations. The iterative process must haltat some point. A slow change halting criteria is evaluated in step 700.If the slow change per iteration in the collision score occurs, the slowchange count is incremented by one in step 705. If the slow change periteration does not occur, the slow change variable is reset to zero instep 710. A short-term oscillation halting criteria is evaluated in step715. If the short-term oscillation in the collision score occurs, theshort-term oscillation count is incremented by one in step 720. If theshort-term oscillation does not occur, the short-term oscillation countis reset to zero in step 725. The previous values of the collision scoreare stored in step 730. Step 730 also increments the iteration count byone. Here, an iteration is one cycle of the anti-collision algorithmthat includes routines 40, 45, 50, and 60. Example rules tested at step735 to halt the procedure follow:

-   -   1) the evaluation function is below a minimum value;    -   2) the number of iterations is greater than a maximum value;    -   3) the evaluation function changes less than a minimum        percentage of the previous iteration for more than a set number        of iterations; and    -   4) the evaluation function oscillates for more than a set number        of consecutive iterations.

If none of these conditions is met, the anti-collision algorithm isrepeated in step 740, noting that labels may move several times beforethe iterations stop. A label's new position is stored in its parameterlist at the time a label is moved. The original position is alwaysavailable in the label's parameter list.

Routine 80, as shown in FIG. 13, adjusts label properties. At thispoint, labels will not be moved because the halting criteria have beensatisfied. However, some labels may still overlap. Routine 80 begins instep 800 by setting the DRAW flag to TRUE for every label. Step 805performs cycling through label pairs. In step 810, each label of thecurrent pair is tested to see if it has too much of its area outside themap or if it is completely outside the map. This avoids unnecessarycalculation for labels that are not used. Labels that have some or allof their area outside the map have their DRAW flag set to FALSE in step815. The overlap test (routine 45) is performed in step 820 on thoselabel pairs for which neither have any area outside the map. If nooverlap occurs between the two labels being tested, then another uniquepair of labels is fetched in step 805.

Otherwise, go to step 825. In step 825, if both labels have MUSTDRAW=TRUE, then go to step 840. Otherwise, go to step 830. In step 830,if the first label has MUST DRAW=TRUE, then go to step 840. Otherwise,go to step 835. In step 835, if the second label has MUST DRAW=TRUE,then go to step 845. Otherwise, go to step 840. In step 840, the secondlabel has its draw flag set to DRAW=FALSE. In step 845, the first labelhas its draw flag set to DRAW=FALSE. Here, the first label is higher onthe list of labels than the second label.

These flags are in the label's parameter list. The MUST DRAW flag is setby the caller. If the DRAW flag is true, this procedure will draw thelabel. If the DRAW is false, this procedure will not draw the label. Forany pair of overlapping labels, the following somewhat arbitrary rulesdetermine the final state of a label's DRAW flag:

-   -   1) If one label has MUST DRAW=TRUE, that label sets DRAW=TRUE,        and the second label sets DRAW=FALSE.    -   2) If both labels have MUST DRAW=TRUE, the label higher on the        list of label priority sets DRAW=TRUE, and the other label sets        DRAW=FALSE. Note that this will hold for labels of equal        priority.    -   3) If neither label has MUST DRAW=TRUE, the label higher on the        list of label priority sets DRAW=TRUE, and the other label sets        DRAW=FALSE. Note that this will hold for labels of equal        priority.

The label priority list and the overlap test are described in precedingsections of the description of the entire anti-collision procedure.

After label properties are adjusted, control is returned to the caller,in step 900 of FIG. 14.

The above-described logic is further shown in the following pseudo-codewith comments.

Pseudo-Code for the Evaluation Function, the Halting Criteria, and theAdjustment of Label Properties

List of pseudo-code variables collision_score - the sum of theevaluation function after each Iteration previous_collision_score - thecollision score from the previous Iterationprevious_previous_collision_score - the collision score from twoiterations ago iteration_count - number of times the anti-collisionprocedure has Looped slow_change_count - number of iterations ofcontinuous slow change of collision score oscillation_count - number ofiterations of continuous oscillation of collision scorepriority_of_most_important_label - numerical priority value of the mostimportant label priority_range - the difference between the priority ofthe least and the most important labels. This number is non-negative.adjusted_priority_1 - the label 1 priority modified to make it work inthe evaluation function // Initialize halting criteria variablespriority_range = priority_of_least_important_label -priority_of_most_important label // initialize these two variables tolarge numbers previous_collision_score = Very Large Numberprevious_previous_collision_score = Very Large Number iteration_count =0 slow_change_count = 0 oscillation_count = 0 //------ The above must bedone at the top of the procedure --------// // Evaluation Function------------------------------------------------------- collision_score= 0 // these loops go thought label priority list for i = first label tolast label  if( label i flag LABEL_TOO_MUCH_OUTSIDE_PORTRAIT = TRUE   ORlabel i flag LABEL_OUTSIDE_PORTRAIT = TRUE ) next i  for j = label i+1to last label  if( label j flag LABEL_TOO_MUCH_OUTSIDE_PORTRAIT = TRUE  OR label j flag LABEL_OUTSIDE_PORTRAIT = TRUE ) next j  if( label iand label j overlap )  {   // Adjust the label priorities to make theevaluation function work  properly.   // Note that the highest prioritylabels are assigned the lowest numbers and   // priorities may bepositive or negative.   adjusted_priority_1 = 1 + priority_range - (label_1_priority - priority_of_most_important_label )  adjusted_priority_2 = 1 + priority_range - ( label_2_priority -priority_of_most_important_label )   collision_score = collision_score +(adjusted_priority_1)*(adjusted_priority_1) +(adjusted_priority_2)*(adjusted_priority_2)  }  next j next i // HaltingAlgorithm --------------------------------------- // is there slowchange ? if(collision_score <= previous_collision_score AND  collision_score > 0.98*previous_collision_score) {  slow_change_count= slow_change_count + 1 } Else {  slow_change_count = 0 } // is thereoscillation ? if( (collision_score > previous_collision_score AND  previous_collision_score < previous_previous_collision_score ) OR  (collision_score < previous_collision_score AND  previous_collision_score > previous_previous_collision_score ) ) { oscillation_count = oscillation_count + 1 } Else { oscillation_count =0 } iteration_count = iteration_count + 1previous_previous_collision_score = previous_collision_scoreprevious_collision_score = collision_score if(collision_score = 0) gotoADJUST_LABEL_PARAMETERS if(iteration_count > 20) gotoADJUST_LABEL_PARAMETERS if(slow_change_count > 4) gotoADJUST_LABEL_PARAMETERS if(oscillation_count > 6) gotoADJUST_LABEL_PARAMETERS goto Start of Next IterationADJUST_LABEL_PARAMETERS: //---------------------------------------------// set label flag DRAW = TRUE for all labels for i = first label to lastlabel  label_i_DRAW = TRUE next i  // these loops go thought labelpriority list and set the draw flag for i = first label to last label if( label i flag LABEL_TOO_MUCH_OUTSIDE_PORTRAIT = TRUE   OR label iflag LABEL_OUTSIDE_PORTRAIT = TRUE )  {   label_i_DRAW = FALSE   next i }  for j = label i+1 to last label   if( label j flagLABEL_TOO_MUCH_OUTSIDE_PORTRAIT =    TRUE OR label j flagLABEL_OUTSIDE_PORTRAIT = TRUE )   {    label_j_DRAW = FALSE    next j  }   if( label i and label j overlap )   {    if ( label_i_MUST_DRAW =TRUE AND label_j_MUST_DRAW =    TRUE )    {     label_j_DRAW = FALSE   }    else if ( label_i_MUST_DRAW = TRUE )    {     label_j_DRAW =FALSE    }    else if ( label_j_MUST_DRAW = TRUE )    {     label_i_DRAW= FALSE    }    Else    {     label_j_DRAW = FALSE    }   }   next j next i  return to caller

While the particular SYSTEM AND METHOD FOR LABELING MAPS as herein shownand described in detail is fully capable of attaining theabove-described objects of the invention, it is to be understood that itis the presently preferred embodiment of the present invention and isthus representative of the subject matter which is broadly contemplatedby the present invention, that the scope of the present invention fullyencompasses other embodiments which may become obvious to those skilledin the art, and that the scope of the present invention is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular means “at least one”. Allstructural and functional equivalents to the elements of theabove-described preferred embodiment that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the presentclaims. Moreover, it is not necessary for a device or method to addresseach and every problem sought to be solved by the present invention, forit to be encompassed by the present claims. Furthermore, no element,component, or method step in the present disclosure is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the claims.

The invention claimed is:
 1. A method for placing labels on a maputilizing a computer system, the computer system programmed to performsteps of the method, comprising: retrieving an association of each ofthe labels with a respective target feature on the map without regard toother of the labels or features of the map, retrieving properties of thefeatures of the map, retrieving properties of the labels, pulling thelabels within boundaries of the map, ordering the labels in rank ofdescending priority, selecting halting criteria parameters includingiteration count, slow change count, and oscillation count, iterating thefollowing steps, (a) to (f): (a) determining if all label pairs havebeen tested, and if all the label pairs have been tested proceeding tostep (d), (b) cycling through the label pairs, testing whether pairmembers overlap each other, and, if the members do not overlap, thenproceeding to step (a), (c) moving a second member of an overlappinglabel pair to a location where there is no overlap with any label, or toa location where there is overlap with one or more labels of lesserpriority than a first label of the label pair, (d) performing anevaluation function to calculate a collision score, (e) executing ahalting procedure using an iteration number, a respective previouscollision score, and the collision score, (f) comparing a result of theexecuting to the halting criteria parameters to determine if the movingthe labels is to be halted, and, if the moving is not to be halted,proceeding to step (a), else proceeding to the following step,eliminating the labels which cannot be placed on the map withoutoverlapping other of the labels with higher priority, adjusting theproperties of the labels, and placing onto the map remaining labels inrespective computed locations.
 2. The method of claim 1 wherein thepulling labels within map boundaries comprises: determining whether eachof the labels is wholly within the boundaries of the map, determining,for labels not wholly within the boundaries of the map, what fraction ofan area of each of the labels is within the boundaries of the map, andmoving each of the labels within the boundaries of the map, if thefraction of the area of each of the labels outside the boundaries of themap is less than a predetermined value, wherein placing onto the map theremaining labels comprises placing onto the map labels that have beenmoved within the boundaries of the map.
 3. The method of claim 1 whereinthe testing whether pair members overlap each other comprises: choosinga first label and a second label to compare, associating the first labelwith a region of a first convex planar polygon, associating the secondlabel with a region of a second convex planar polygon, finding maximumextents of the first convex planar polygon and the second convex planarpolygon respectively associated with the first label and the secondlabel, comparing the maximum extent of the first polygon with themaximum extent of the second polygon and, if the extents do not overlap,concluding that the pair members do not overlap each other, testingvertices of the first polygon with edges forming a perimeter of thesecond polygon and, if any vertex is within the second polygon, thenconcluding that the pair members overlap each other, and testing eachedge of the first polygon with each edge of the second polygon, and, ifany edges being tested intersect, then concluding that the pair membersoverlap each other.
 4. The method of claim 3 wherein the testing thevertices of the first polygon with the edges forming the perimeter ofthe second polygon comprises: traversing the perimeter of the secondpolygon, obtaining equations of lines containing the edges forming theperimeter of the second polygon, testing the vertices of the firstpolygon with the equations of the lines containing the edges forming theperimeter of the second polygon until all the vertices of the firstpolygon are tested, and concluding that the label pair overlap if anyvertex of the first polygon is within a boundary of the second polygonas determined by the equations.
 5. The method of claim 3 wherein thetesting each edge of the first polygon with each edge of the secondpolygon comprises: obtaining equations of lines containing edges of thefirst polygon, obtaining equations of lines containing edges of thesecond polygon, calculating intersection points of the edges of thefirst polygon and the edges of the second polygon, determining if thepoints lie on any of the edges of the first polygon or any of the edgesof the second polygon, and concluding that if at least one of the pointslies on any of the edges of the first polygon or any of the edges of thesecond polygon then the label pair overlap.
 6. The method of claim 1wherein the performing the evaluation function comprises: cyclingthrough label pairs, testing whether members of a current label pairoverlap, checking whether either label of the pair is too far outsidethe boundaries of the map or completely outside of the boundaries of themap, and performing the calculation of the collision score of a labeloverlap.
 7. The method of claim 6 wherein the to determine if the movingthe labels is to be halted comprises: testing if: (a) the collisionscore of the label overlap is zero, or (b) a consecutive number ofiterations of slow changes exceeds the slow change count, or (c) anumber of oscillations exceeds the oscillation count, or (d) a number ofiterations exceeds the iteration count.
 8. The method of claim 1 whereinthe adjusting the properties of the labels comprises cycling througheach label pair, testing whether each member of the pair overlap,eliminating a second member of the each label pair if the second memberoverlaps a first member of the each label pair, and eliminating thelabels not pulled into the boundaries of the map.
 9. The method of claim1 wherein the step of moving the second member of an overlapping labelpair and the step of eliminating the labels comprise: moving a secondmember of an overlapping label pair, which overlap other of the labelsof higher priority or equal priority, whenever possible to locationswhere there is no overlap; or, if not possible, to where there isoverlap with one or more of the labels of lesser priority or equalpriority; eliminating the labels of lesser priority where there isoverlap with the labels of higher priority; and eliminating labels whichoverlap labels of equal priority so that one label remains.
 10. Anon-transitory computer storage medium storing computer executableinstructions for performing the method of claim
 1. 11. The medium ofclaim 10 wherein the pulling labels within map boundaries comprises:determining whether each of the labels is wholly within the boundariesof the map, determining, for labels not wholly within the boundaries ofthe map, what fraction of an area of each of the labels is within theboundaries of the map, and moving each of the labels within theboundaries of the map, if the fraction of the area of each of the labelsoutside the boundaries of the map is less than a predetermined value,wherein placing onto the map the remaining labels comprises placing ontothe map labels that have been moved within the boundaries of the map.12. The medium of claim 10 wherein the testing whether pair membersoverlap each other comprises: choosing a first label and a second labelto compare, associating the first label with a region of a first convexplanar polygon, associating the second label with a region of a secondconvex planar polygon, finding maximum extents of the first convexplanar polygon and the second convex planar polygon respectivelyassociated with the first label and the second label, comparing themaximum extent of the first polygon with the maximum extent of thesecond polygon and, if the extents do not overlap, concluding that thepair members do not overlap each other, testing vertices of the firstpolygon with edges forming a perimeter of the second polygon and, if anyvertex is within the second polygon, then concluding that the pairmembers overlap each other, and testing each edge of the first polygonwith each edge of the second polygon, and, if any edges being testedintersect, then concluding that the pair members overlap each other. 13.The medium of claim 12 wherein the testing the vertices of the firstpolygon with the edges forming the perimeter of the second polygoncomprises: traversing the perimeter of the second polygon, obtainingequations of lines containing the edges forming the perimeter of thesecond polygon, testing the vertices of the first polygon with theequations of the lines containing the edges forming the perimeter of thesecond polygon until all the vertices of the first polygon are tested,and concluding that the label pair overlap if any vertex of the firstpolygon is within a boundary of the second polygon as determined by theequations.
 14. The medium of claim 12 wherein the testing each edge ofthe first polygon with each edge of the second polygon comprises:obtaining equations of lines containing edges of the first polygon,obtaining equations of lines containing edges of the second polygon,calculating intersection points of the edges of the first polygon andthe edges of the second polygon, determining if the points lie on any ofthe edges of the first polygon or any of the edges of the secondpolygon, and concluding that if at least one of the points lies on anyof the edges of the first polygon or any of the edges of the secondpolygon then the label pair overlap.
 15. The medium of claim 10 whereinthe performing the evaluation function comprises: cycling through labelpairs, testing whether members of a current label pair overlap, checkingwhether either label of the pair is too far outside the boundaries ofthe map or completely outside of the boundaries of the map, andperforming the calculation of the collision score of a label overlap.16. The method of claim 15 wherein the to determine if the moving thelabels is to be halted comprises: testing if: (a) the collision score ofthe label overlap is zero, or (b) a consecutive number of iterations ofslow changes exceeds the slow change count, or (c) a number ofoscillations exceeds the oscillation count, or (d) a number ofiterations exceeds the iteration count.
 17. The medium of claim 10wherein the adjusting the properties of the labels comprises cyclingthrough each label pair, testing whether each member of the pairoverlap, eliminating a second member of the each label pair if thesecond member overlaps a first member of the each label pair, andeliminating the labels not pulled into the boundaries of the map. 18.The medium of claim 10 wherein the step of moving the second member ofan overlapping label pair and the step of eliminating the labelscomprise: moving a second member of an overlapping label pair, whichoverlap other of the labels of higher priority or equal priority,whenever possible to locations where there is no overlap; or, if notpossible, to where there is overlap with one or more of the labels oflesser priority or equal priority; eliminating the labels of lesserpriority where there is overlap with the labels of higher priority; andeliminating labels which overlap labels of equal priority so that onelabel remains.
 19. A computer system for automatically labeling a map inaccordance predefined label positioning and placement criteria, the mapincluding a plurality of regions encompassing points with said regionand bounded by region boundary points to be labeled with a correspondinglabel in accordance with said label positioning and placement criteria,said system comprising: input cans for inputting map data includingregion data for said plurality of regions to be labeled and label dataincluding said corresponding label for each of said plurality ofregions, first memory means for storing said map data and said regiondata, processor means responsive to a control program for generatingdigital signals corresponding to approximate label positions for each ofsaid regions satisfying said label positioning criteria and digitalsignals denoting final label positions for each of said locationssatisfying said label placement criteria, said processor means beingadapted to: retrieving an association of each of the labels with arespective target feature on the map without regard to other of thelabels or features of the map, retrieving properties of the features ofthe map, retrieving properties of the labels, pulling the labels withinboundaries of the map, ordering the labels in rank of descendingpriority, selecting halting criteria parameters including iterationcount, slow change count, and oscillation count, iterating the followingsteps, (a) to (f): (a) determining if all label pairs have been tested,and if all the label pairs have been tested proceeding to step (d), (b)cycling through the label pairs, testing whether pair members overlapeach other, and, if the members do not overlap, then proceeding to step(a), (c) moving a second member of an overlapping label pair to alocation where there is no overlap with any label, or to a locationwhere there is overlap with one or more labels of lesser priority than afirst label of the label pair, (d) performing an evaluation function tocalculate a collision score, (e) executing a halting procedure using aniteration number, a respective previous collision score, and thecollision score, (f) comparing a result of the executing to the haltingcriteria parameters to determine if the moving the labels is to behalted, and, if the moving is not to be halted, proceeding to step (a),else proceeding to the following step, eliminating the labels whichcannot be placed on the map without overlapping other of the labels withhigher priority, adjusting the properties of the labels, and placingonto the map remaining labels in respective computed locations.
 20. Thecomputer system as claimed in claim 19, further comprising display meansfor displaying a graphic image of said map data together with a graphicimage generated from said digital signals corresponding to the finallabel positions of each label.
 21. The computer system of claim 19wherein the pulling labels within map boundaries comprises: determiningwhether each of the labels is wholly within the boundaries of the map,determining, for labels not wholly within the boundaries of the map,what fraction of an area of each of the labels is within the boundariesof the map, and moving each of the labels within the boundaries of themap, if the fraction of the area of each of the labels outside theboundaries of the map is less than a predetermined value, whereinplacing onto the map the remaining labels comprises placing onto the maplabels that have been moved within the boundaries of the map.
 22. Thecomputer system of claim 19 wherein the testing whether pair membersoverlap each other comprises: choosing a first label and a second labelto compare, associating the first label with a region of a first convexplanar polygon, associating the second label with a region of a secondconvex planar polygon, finding maximum extents of the first convexplanar polygon and the second convex planar polygon respectivelyassociated with the first label and the second label, comparing themaximum extent of the first polygon with the maximum extent of thesecond polygon and, if the extents do not overlap, concluding that thepair members do not overlap each other, testing vertices of the firstpolygon with edges forming a perimeter of the second polygon and, if anyvertex is within the second polygon, then concluding that the pairmembers overlap each other, and testing each edge of the first polygonwith each edge of the second polygon, and, if any edges being testedintersect, then concluding that the pair members overlap each other. 23.The computer system of claim 22 wherein the testing the vertices of thefirst polygon with the edges forming the perimeter of the second polygoncomprises: traversing the perimeter of the second polygon, obtainingequations of lines containing the edges forming the perimeter of thesecond polygon, testing the vertices of the first polygon with theequations of the lines containing the edges forming the perimeter of thesecond polygon until all the vertices of the first polygon are tested,and concluding that the label pair overlap if any vertex of the firstpolygon is within a boundary of the second polygon as determined by theequations.
 24. The computer system of claim 22 wherein the testing eachedge of the first polygon with each edge of the second polygoncomprises: obtaining equations of lines containing edges of the firstpolygon, obtaining equations of lines containing edges of the secondpolygon, calculating intersection points of the edges of the firstpolygon and the edges of the second polygon, determining if the pointslie on any of the edges of the first polygon or any of the edges of thesecond polygon, and concluding that if at least one of the points lieson any of the edges of the first polygon or any of the edges of thesecond polygon then the label pair overlap.
 25. The computer system ofclaim 19 wherein the performing the evaluation function comprises:cycling through label pairs, testing whether members of a current labelpair overlap, checking whether either label of the pair is too faroutside the boundaries of the map or completely outside of theboundaries of the map, and performing the calculation of the collisionscore of a label overlap.
 26. The computer system of claim 25 whereinthe to determine if the moving the labels is to be halted comprises:testing if: (a) the collision score of the label overlap is zero, or (b)a consecutive number of iterations of slow changes exceeds the slowchange count, or (c) a number of oscillations exceeds the oscillationcount, or (d) a number of iterations exceeds the iteration count. 27.The computer system of claim 19 wherein the adjusting the properties ofthe labels comprises cycling through each label pair, testing whethereach member of the pair overlap, eliminating a second member of the eachlabel pair if the second member overlaps a first member of the eachlabel pair, and eliminating the labels not pulled into the boundaries ofthe map.
 28. The computer system of claim 19 wherein the step of movingthe second member of an overlapping label pair and the step ofeliminating the labels comprise: moving a second member of anoverlapping label pair, which overlap other of the labels of higherpriority or equal priority, whenever possible to locations where thereis no overlap; or, if not possible, to where there is overlap with oneor more of the labels of lesser priority or equal priority; eliminatingthe labels of lesser priority where there is overlap with the labels ofhigher priority; and eliminating labels which overlap labels of equalpriority so that one label remains.